Field studies were conducted during 1999 and 2000 to compare weed control after fall and early-preplant (EPP) herbicide applications in no-till soybean. Three residual treatments (chlorimuron plus metribuzin, chlorimuron plus sulfentrazone, and metribuzin) were applied at two rates and timings (fall and 30 d EPP) either alone or in combination with glyphosate and 2,4-D. The addition of glyphosate and 2,4-D to fall-applied residual herbicides significantly increased control of common chickweed, annual bluegrass, cressleaf groundsel, and shepherd's-purse. The effect of application rate on weed control was species dependent. Fall-applied residual herbicides were comparable with EPP treatments with respect to winter annual weed control; however, at planting control of summer annual weed species with fall treatments was less consistent compared with EPP residual herbicides.
Nomenclature: Chlorimuron; glyphosate; metribuzin; sulfentrazone; 2,4-D ester; annual bluegrass, Poa annua L. #3 POAAN; common chickweed, Stellaria media L. Vill. # STEME; cressleaf groundsel, Senecio glabellus Poir. # SENGL; shepherd's-purse, Capsella bursa-pastoris (L.) Medicus # CAPBP; soybean, Glycine max (L.) Merr.
Additional index words: AMATA, AMBEL, AMBTR, CHEAL, fall applied, LAMAM, LAMPU, no till, residual control, winter annuals.
Abbreviation: EPP, early preplant.